Manual preset timer

ABSTRACT

A manual preset interval timer in which drag on the timer cam shaft is eliminated after the timer is set so that it can run back to the OFF position with almost zero torque applied. The timer cam during the initial setting stroke lifts a switch operator through a pawl to timing position where it is held by a latch. The pawl and cam are arranged to apply a component of force to the pawl to hold it in driving position during the setting stroke. This component of force instantly disappears at the end of the setting stroke to unload the cam.

United States Patent 1 in l 3,922,924 Harris Dec. 2, 1975 l l MANUAL PRESET TIMER [75] Inventor: John L. Harris, Clearwater, Fla. Primary Exammer AHan Hcrrmann [73] Ass1gnee: Deltrol Corporatlon, Bellwood, Ill. ABSTRACT [22] Flled: 1974 A manual preset interval timer in which drag on the [21] Appl. No.: 534,222 timer cam shaft is eliminated after the timer is set so that it can run back to the OFF position with almost 52 us. Cl. 74/35; 200/39 R torque P T durmg the 2 setting stroke lifts a switch operator through a pawl to [51] Int. Cl. GOSG 17/00 timing position Where it is held y a atch The p [58] Field of Search 74/35; l37/624.22; d I f f 200/38 B 39 R 39 A an cam are arranged to y a component 0 orce to the pawl to hold it in driving position during the setting stroke. This component of force instantly disap- References cued pears at the end of the setting stroke to unload the UNITED STATES PATENTS cam 3,489,015 I/197O Harris 74/3.5 3,699,281 10/1972 Harris 200/39 R 10 Clams, 6 Drawmg Flgures U.S. Patfint Dec. 2, 1975 3,922,924

MANUAL PRESET TIMER BACKGROUND OF THE INVENTION This invention relates in general to timing devices and more particularly to timers of the manual preset type.

Such timers are used for turning off appliances after a desired time. The user turns a knob which drives a cam lifting a cam follower to close the timer switch, starting the appliance and the timer motor, which drives the cam back to the off position. A friction clutch is necessary between the motor and cam shaft to allow setting of the cam shaft without damage to the motor and gearing. The motor must drive the cam shaft back to the off position through this friction clutch and its torque must be high enough to overcome the friction load of the follower on the cam or the timer will fail.

In some applications it is necessary to use both short timings and long timings. For example, in micro-wave ovens, some items will heat in a minute or two while others require up to 30 minutes. When a uniform scale thirty minute timer is set down to two minutes, the inaccuracy in setting becomes a large percentage of the desired time, giving unsatisfactory results. This makes it desirable to use a logarithmic or expanded scale timer. This type of timer utilizes a pair of eccentric gears meshing together to drive the cam shaft at a variable rate which increases in speed as the timer approaches the OFF position. This gives relatively large dial divisions for short timings where accuracy is needed and relatively small dial divisions for long timings where accuracy is not needed.

This type of timer involves a problem with the friction clutch. The torque must be set high enough to drive the timer to the OFF position with a reasonable factor of safety. Due to the variable ratio gears, turning the timer shaft to its maximum setting slips the friction clutch approximately six times as fast as occurred at the start of the setting stroke. This makes it about six times as hard to turn the knob, making the timer hard to set and giving a rough feeling as the eccentric gear teeth bump over each other with the heavy loading.

BRIEF SUMMARY OF THE INVENTION The primary object of the invention is the provision ofa timer mechanism in which the timer cam shaft runs unloaded and trips the timer switch to its off position with a minimum of force required, this reducing the torque required in the friction clutch and making the timer easier to set.

In accordance with the invention, the timer cam shaft drives the timer switch operator to timing position through a pawl when the timer shaft is turned from the OFF position. A latch holds the timer switch in timing position and the pawl is rendered incapable of applying pressure from the switch to the cam shaft at theinstant the setting stroke of the switch operator is completed. This insures that the cam shaft is always unloaded when driven by the friction clutch back to the OFF position where it releases the latch to open the switch.

A further object of the invention is to provide a timing mechanism requiring but slight force to trip the switch at the OFF position.

This is achieved by arranging the latch and switch operator so as to provide a substantial mechanical advantage at the point where the latch is contacted by the timer cam.

Other objects will appear from the following detailed description and appended claims.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a front view of a manual preset timer embodying the invention, with the front cover removed and showing the parts in the positions assumed at timed-out";

FIG. 2 is a side internal view of FIG. 1;

FIG. 3 is a fragmentary view showing the parts in the positions assumed during the manual setting stroke;

FIG. 4 is a similar fragmentary view showing the positions of the parts during a time cycle;

FIG. 5 is a fragmentary view showing the driving pawl in released position;

FIG. 6 is a partial bottom view of FIG. 1.

Referring to FIGS. 1 and 2, reference character 1 indicates generally a timer housing including a front plate 2, a back plate 3, side walls 4 and 5 and a switch panel 6. The switch panel 6 supports a switch including a switch blade 7 carrying a movable contact 8 cooperating with a stationary contact 9 carried by a bracket 10. The contact bracket 10 is carried by the switch panel 1 by suitable means not shown. Switch blade 7 is biased downwardly as seen in FIG. 1 for causing contact 8 to engage contact 9. This switch blade is moved upwardly against its bias by means of a switch operator or controller operating means generally indicated as 11. This switch operator includes a hub 12 fitting over a stud l3 and carrying a lever portion 14 which extends to the left as seen in FIG. 1 and includes an edge 15 engaging the switch blade 7. The switch operator also includes a latch engaging surface 16 carried by an offset portion 17 extending under the contact bracket 10. This offset portion 17 is preferrably arranged to engage the contact bracket 10 which limits its upward stroke as shown in FIG. 1. This switch operator 11 is biased counterclockwise or upwardly by means of a torsion spring 18 carried by the hub 12, one leg of this spring engaging sidewall 5 and the other leg engaging a stud 20 at the rear of the operator.

The switch operator 11 is rotated counterclockwise through its driven stroke from the timed-out position shown in FIG. 1 to its timing position shown in the other figures by means of a pawl 22 which is pivoted on a stud 23 formed on the switch operator 11. This pawl 22 includes a hub 24 fitting over stud 23 and carrying a torsion spring 25, one end bearing on a stud 26 on the switch operator and the other end bearing on a stud 27 formed on the pawl. The spring 25 serves to bias the pawl 22 in a clockwise direction into a predetermined relationship with the switch operator as determined by a stop ear 29 engaging a stop pin 30 formed on the switch operator. The pawl 22 extends downwardly and is formed with a curved camming surface 31 which terminates abruptly at a releasing surface 32 which merges with a lifting camming surface 33.

As shown in FIG. 2, the latching surface 16 of the switch operator extends rearwardly to a point adjacent the back plate 3 and is engaged by a latch means generally indicated as 35 (FIG. 1 This latch means includes a hub 36 carried on a stud 37 attached to the back plate, the hub carrying a spring 38 one end of which bears against the stationary stud 39, and the other end bearing on a stud 40 carried by the latch means. The latch 35 also includes an upwardly extending latching lever 41 which terminates in a latching surface 42 cooperating with the latching surface 16 on the switch operator. The latch 35 also includes an operating arm 44 which extends to the right adjacent the back plate 3 as shown in FIG. 6. The latch also includes an outwardly extending operating portion 45 which extends upwardly to a point adjacent the camming surface 31 of pawl 22. l

The lug 45 and camming surface 31 are actuated by a timing means including a cam 46"having a lob'e 47, one side of this lobe engaging lug 45 on the latch and the other side of the lobe engaging the-lifting cam surface 31 on the pawl. The cam 46 is carried by a main shaft 48 which is journaled between the front and back plates and extends outwardly through the front plate to the usual manual setting knob not shown. The timing means preferrably includes an eccentric or log gear 49 which is driven by a second eccentric gear 50 which is driven through a friction clutch 51 by a gear 52 meshing with the pinion 53 of an electric timer motor (not shown).

OPERATION The parts in FIG. 1 are shown in the positions assumed at the end of a timing cycle. Lobe 47 of the cam has moved the latch to the released position shown which has allowed the switch operator to be rotated up wardly by its spring causing the switch operating surface 15 to engage blade 7 and open the contacts.

When the timer is set for a time cycle, the shaft 48 is turned clockwise by the usual setting knob, this causing the cam lobe 47 to engage the camming'or lifting surface 31 of the pawl 22 as shown in FIG. 3. As shown in this figure the camming surface 31 is plotted so as to present a surface substantially at a right angle to the path of movement of the engaging surface of the cam lobe 47. This creates a force on the switch operator and pawl assembly represented by line A-B. This force has a component A-C tending to rotate the pawl 22 clockwise causing the stop portion 29 to engage lug 30 on the switch operator. This force A-B also operates on a lever arm A-D rotating the switch operator counterclockwise about it's pivot 13 against the action of the biasing spring 18.

From the foregoing it will be apparent that the manual setting operation of turning cam 46 clockwise results in counterclockwise rotation of the switch operator assembly. This allows contacts 8 and 9 to engage and also brings the latching surface 16 clear of the latching surface 42 which allows the latch 35 to move into latching position as shown in FIG. 3. This manual setting rotation of the camshaft is permitted by slipping of the friction clutch 51 as well known in the art. 'On continued manual clockwise rotation of the camshaft the cam lobe 47 rides off the lifting surface 31 and under the surface 32 as shown in FIG. 5. At this point the force acting along line A-B disappears and the switch operator assembly is free to rotate clockwise under its biasing spring until latching surface 16 engages with surface 42 on latch 35. This position is shown in FIG. 4. It will be noted that the switch contacts are still closed and that the cam may be rotated to its maximum timing position as shown. As the timer switch is now closed the timer motor (not shown) will drive the cam 46 counterclockwise back to the position shown in FIG. 1. As the lobe 47 approaches the timed-out position it engages the camming or lifting surface 33 on the pawl, lifting it to the position shown in FIG. 5. At this time the pawl is free to rotate about its pivot 23 and the light return spring 25 is the only force opposing this movement. This requires very little torque. As the cam approaches the timed-out position lobe 47 engages extension of the latch lever rotating it counterclockwise about its pivot 37 toward the releasing position shown in FIG. 1. When the latching surface 42 on the latch rides off latching surface 16 on the switch operator, the switch operator spring 18 rotates the operator with snap action to the position shown in FIG. 1 in which the movable contact 8 is separated from the stationary contact 9.

The torque on cam 46 required to release the latch 35 is very low due to the mechanical advantage provided. It should be noted that the switch operator 11 is pivoted on the right side of the timing means or cam 46 and extends to the left side thereof where the latch engaging surface 16 is located. Also the latch 35 is pivoted on the left side of the timing means and includes the elongated leg 44 extending to the other side of the cam 46 in the path of cam lobe 47. This arrangement in effect provides a compound leverage at the latch operating portion 45, this giving substantial mechanical advantage to the cam lobe and permitting the latch to be released with very little operating force from the cam.

Summarizing, the cam lobe and pawl provide a one way drive means for driving the switch operator through its driven stroke from the timed-out position shown in FIG. 1 to the latch engaging position shown in'FlG. 3. During this driven stroke the engaging means consisting of lobe 47 and camming surface 31 provide a component of force for driving the switch operator and maintaining the pawl in fixed position relative to the switch operator. As soon as lobe 47 rides off camming surface 31 onto the neutral surface 32 this component of force disappears and the pawl is free to release from lug 30 allowing the switch operator to assume its timing or latched position as shown in FIG. 4. As the timer runs back to its timed-out position there is no load on the cam as the pawl is not even touching it as shown in FIG. 4. As the timer approaches its timed-out position it rides under pawl 22 as shown in FIG. 5, this requiring very little force as the only resistance is the light spring 25. On continued movement of the timing means it rotates the latch to released position, this requiring very little force as it is only an unlatching action with a substantial mechanical advantage.

From the foregoing it will be seen that the invention provides an arrangement in which the force required of the timer cam in reaching timed-out position is extremely small. This permits the friction clutch to be set for a very low torque which makes it easy for the timer to be set to its maximum position even with the log gearing. This arrangement also provides for an additional reliability inasmuch as it avoids the largest single cause of manual preset timer failures which is slipping of the friction clutch.

While a preferred form of the invention has been shown and described it will be obvious that many changes may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. In a timing device, controller operating means movable through a predetermined stroke between a timing position and a timed-out position, timing means having a timedout position and being movable in one direction from its timed-out position to a timing position. said timing means being constructed and arranged to run in the opposite direction back to its timed-out position, means including latch means for holding the operating means in timing position when the latch means is engaged and for returning the operating means to timed-out position when the latch means is disengaged, one way drive means between the timing means and operating means and arranged to move the operating means through a driven stroke from timedout position to timing position for engagement of the latch means as said timing means is moved in said one direction from its timed-out position, said one way drive means including a pawl bodily carried by one of said two first mentioned means and engaging the other, said pawl and its engaging means being constructed and arranged to provide a component of force holding the pawl in driving position while the operating means is being moved through its driven stroke and to reduce said component of force at the end of said driven stroke so that the pawl is ineffective to hold the operating means in timing position, and means actuated by the timing means on reaching its timed-out position for releasing the latch means.

2. The combination recited in claim 1 in which the pawl is pivoted to the operating means and the timing means includes a cam having a surface engaging and lifting the pawl.

3. The combination recited in claim 1 in which the pawl is pivoted to the operating means and the timing means includes a cam shaft having a cam segment, one part of said segment being arranged to engage and lift the pawl and another part of said segment being arranged to engage and release the latch means.

4. The combination recited in claim 1 in which the operating means is a lever having a pivot on one side of the timing means, said lever extending to the other side of the timing means and having a latch engaging surface, said latch means including a latch lever having a pivot on said other side of the timing means and a latch portion cooperating with said latch engaging surface, said latch lever also having an operating leg extending back to said one side of the timing means and being actuated by said timing means at said one side thereof.

5. The combination recited in claim 1 in which the operating means is a lever and the timing means is a cam shaft said lever being pivoted at one side of the cam shaft and extending to the other side thereof and having a latch engaging surface, said latch means including a latch lever having a pivot on said other side of the cam shaft and a latch portion cooperating with said latch engaging surface, said latch lever having an operating leg extending back to said one side of the cam shaft and being actuated by the cam shaft at a location on said one side thereof, said pawl being pivoted to the operating means and extending to a point adjacent said location.

6. The combination recited in claim 1 in which the pawl is formed with two surfaces at substantial angles to each other, one surface providing the component of force holding the pawl in driving position during the stroke of the operating means and the other surface being contacted at the end of the stroke terminating said component of force.

7. The combination recited in claim 6 in which the pawl is pivoted to the operating means and is engaged by the timing means during the driven stroke of the operating means.

8. The combination recited in claim 5 in which the pawl is pivoted to the lever at a point substantially spaced from the location where the latch lever is actuated and extends adjacent to said location, the cam shaft including a camming portion having two sides, one side engaging the pawl and the other side engaging the latch means.

9. The combination recited in claim 8 in which the pawl is formed with two surfaces at substantial angles to each other, one surface providing the component of force holding the pawl in driving position during the driven stroke of the operating means and the other surface being contacted at the end of the stroke, terminating the component of force.

10. The combination recited in claim 9 in which the pawl is in tension during the driven stroke of the operating means and is provided with stop means between it and the operating means lever for determining the location of the pawl relative to the lever during the driven stroke of the lever, the one surface of the pawl being arranged to hold the pawl against the stop means. 

1. In a timing device, controller operating means movable through a predetermined stroke between a timing position and a timed-out position, timing means having a timed-out position and being movable in one direction from its timed-out position to a timing position, said timing means being constructed and arranged to run in the opposite direction back to its timed-out position, means including latch means for holding the operating means in timing position when the latch means is engaged and for returning the operating means to timed-out position when the latch means is disengaged, one way drive means between the timing means and operating means and arranged to move the operating means through a driven stroke from timed-out position to timing position for engagement of the latch means as said timing means is moved in said one direction from its timed-out position, said one way drive means including a pawl bodily carried by one of said two first mentioned means and engaging the other, said pawl and its engaging means being constructed and arranged to provide a component of force holding the pawl in driving position while the operating means is being moved through its driven stroke and to reduce said component of force at the end of said driven stroke so that the pawl is ineffective to hold the operating means in timing position, and means actuated by the timing means on reaching its timed-out position for releasing the latch means.
 2. The combination recited in claim 1 in which the pawl is pivoted to the operating means and the timing means includes a cam having a surface engaging and lifting the pawl.
 3. The combination recited iN claim 1 in which the pawl is pivoted to the operating means and the timing means includes a cam shaft having a cam segment, one part of said segment being arranged to engage and lift the pawl and another part of said segment being arranged to engage and release the latch means.
 4. The combination recited in claim 1 in which the operating means is a lever having a pivot on one side of the timing means, said lever extending to the other side of the timing means and having a latch engaging surface, said latch means including a latch lever having a pivot on said other side of the timing means and a latch portion cooperating with said latch engaging surface, said latch lever also having an operating leg extending back to said one side of the timing means and being actuated by said timing means at said one side thereof.
 5. The combination recited in claim 1 in which the operating means is a lever and the timing means is a cam shaft, said lever being pivoted at one side of the cam shaft and extending to the other side thereof and having a latch engaging surface, said latch means including a latch lever having a pivot on said other side of the cam shaft and a latch portion cooperating with said latch engaging surface, said latch lever having an operating leg extending back to said one side of the cam shaft and being actuated by the cam shaft at a location on said one side thereof, said pawl being pivoted to the operating means and extending to a point adjacent said location.
 6. The combination recited in claim 1 in which the pawl is formed with two surfaces at substantial angles to each other, one surface providing the component of force holding the pawl in driving position during the stroke of the operating means and the other surface being contacted at the end of the stroke terminating said component of force.
 7. The combination recited in claim 6 in which the pawl is pivoted to the operating means and is engaged by the timing means during the driven stroke of the operating means.
 8. The combination recited in claim 5 in which the pawl is pivoted to the lever at a point substantially spaced from the location where the latch lever is actuated and extends adjacent to said location, the cam shaft including a camming portion having two sides, one side engaging the pawl and the other side engaging the latch means.
 9. The combination recited in claim 8 in which the pawl is formed with two surfaces at substantial angles to each other, one surface providing the component of force holding the pawl in driving position during the driven stroke of the operating means and the other surface being contacted at the end of the stroke, terminating the component of force.
 10. The combination recited in claim 9 in which the pawl is in tension during the driven stroke of the operating means and is provided with stop means between it and the operating means lever for determining the location of the pawl relative to the lever during the driven stroke of the lever, the one surface of the pawl being arranged to hold the pawl against the stop means. 